This invention relates to vertical form, fill and seal machines, and in particular to such machines employing stripping of the end seal area. The invention provides a unique means of stripping utilizing staggered wiper members and a unique method of stripping the end seal area.
For many years, manufacturers of vertical form, fill and seal machines have been concerned about seal quality of the packages formed in the equipment. This concern is particularly relevant in the end seal where it is possible for packaged product to be trapped between the surfaces of the sealing jaws when the jaws close to complete the end seals. The trapped product keeps the film surfaces from achieving intimate contact for sealing, and the result is an open or partially open package. This is a particularly serious problem when the product in the package is a food product subject to spoilage or contamination. The problem is worsened when the package is being formed to contain an inert gas for preservation of the product and thus when the integrity of the seal must be without question.
Many stripping devices have evolved over the years. One such device is described in U.S. Pat. No. 4,391,081, assigned to Hayssen Manufacturing Company and now owned by the owner of the present application. This patent discloses a stripping mechanism which is capable of reaching between the open sealing jaws, closing on the film tube, and moving downwardly to force product into the bag below the end seal area before the sealing jaws are closed. The '081 patent is an improvement over the vertical form, fill and seal apparatus disclosed in U.S. Pat. No. 4,288,965 which is also owned by the assignee of the present application.
With the development of servo motor technology, vertical form, fill and seal machines were made more versatile. Servo technology allowed the stripping to take place by first pulling a bag longer than the ultimately-desired package length. Then, the sealing jaws, or other stripping mechanism, are engaged and the film is pulled in the reverse direction through the jaws or the stripping mechanism to strip the end seal area. Such a method is described in U.S. Pat. No. 5,485,772 which is also owned by the assignee of the present invention. A mechanical means for accomplishing the same goal is described in Klinkel U.S. Pat. No. 4,757,668.
With the advent of high speed equipment with a continuously advancing film tube, the stripping process has been made somewhat more complex, but still similar to the reverse stripping process in that the film tube is stripped vertically through the end seal area. In a continuous motion machine, the sealing jaws follow the film for a portion of the bag making cycle, and stripping is accomplished by partially closing the sealing jaws or engaging the stripping mechanism, and then overrunning the film tube for a brief period of time in order to strip the end seal area. The jaws are then closed following stripping to complete formation of the package. In this manner, product is forced into the package while the film is always being pulled in a forward direction, and reversing of the film pull direction is unnecessary.
In all known stripping apparatus and methods, the stripping mechanism employs a series of moving parts. The parts are expensive, and must be properly sized and timed in operation so as not to interfere with the sealing jaws. It is an important advantage to provide a stripping mechanism and method which employs a stripping means having no moving parts.